Faradaic number as a criterion for the promotion effect of external electric field on the heterogeneous oxidative cracking of liquefied petroleum gas on ZSM-5 supported catalyst

Abstract

The oxidative cracking of liquefied petroleum gas (LPG) in the presence of CO2 as oxidant, under a novel catalytic reaction system, with an electric field, was studied over a series of CrHZSM-5, HZSM-5 and NaZSM-5 catalysts. This research is the first report for olefin production with the synergetic effect of zeolite catalysts and external electric field. The prepared catalysts were characterized by XRD, SEM, FTIR, BET, NH3-TPD, H2-TPR and TGA techniques and an impedance analyzer with a potentiostat. Different parameters such as temperature, input electrical current, gap distance, amount of metal loading, oxidant, and GHSV were investigated. The activity was greatly increased by a weak electric field. The XRD pattern showed that the structure of the treated catalysts remained intact while BET results indicated the surface and micropore areas decreased after metal loading on HZSM-5. TPR data exhibited the reduction phenomenon of the catalysts. NH3-TPD analysis determined that Cr/HZSM-5 catalyst has more strong acid sites compared to NaZSM-5 and HZSM-5. According to TGA result, in the presence of an electric field, coke formation is decreased. Electrical conductivity played an important role in the reaction. Faradaic number was used to show the promotion effect of electric field. The results showed the electrons provided by external electric field, metal loading, and catalyst support were drastically promoted LPG to light olefins at 625 °C and 12 mA, which led to 42.58 and 92.12% ethylene yield and conversion, respectively, and 335.07 Faradaic number.